The present invention relates generally to a method for estimating the inlet and outlet air conditions of an HVAC system to determine the load requirements of the system.
The greenhouse gases emitted to the atmosphere by an HVAC system can be reduced by efficiently utilizing electric power. Electric power can be efficiently utilized by employing capacity control that matches the system capacity to the load requirements of the HVAC system. Capacity control utilizes various refrigerant and air conditions to determine the load requirement of the HVAC system. Sensors are generally utilized in an HVAC system to detect the pressure and the temperature of the refrigerant entering and exiting the compressor, the temperature of the refrigerant entering and exiting the evaporator, and the temperature of the air entering the evaporator. Once the load requirements are known, the compressor can be control so that the system capacity matches the load requirements.
The temperature of the air exiting the evaporator and the relative humidity of the air entering and exiting the evaporator also need to be detected to employ capacity control. However, a drawback is that additional sensors must be installed to monitor the temperature of the air exiting the evaporator and the relative humidity of the air entering and exiting the evaporator. In the prior art, humidity sensors, dry bulb sensors, and wet bulb temperature sensors were added to the vapor compression system to monitor these conditions.
There are several drawbacks to installing additional sensors in the HVAC system. For one, employing additional sensors is expensive. Additionally, the measurements provided by some sensors may not be reliable due to the complex dynamics of a thermodynamic system. For example, if a sensor is employed to measure the air temperature of the air exiting the evaporator, the turbulence in the outlet air created by a fan can affect the temperature reading. It would be beneficial to determine the temperature of the air exiting the evaporator and the relative humidity of the air entering and exiting the evaporator without using additional sensors.
Therefore, the present invention provides a method that utilizes existing sensors to provide an accurate estimation of the inlet and outlet air conditions of the evaporator that are needed for capacity control without additional cost to the system and also provides the information needed for the diagnostic/prognostics of the HVAC system as well as overcoming the other drawbacks and shortcomings of the prior art.